Bug summary

If we change the color of a contour set to black by calling CS.set_color('k'), the lines and fill colors are messed up, and the colors of contour labels are not updated to black correspondingly.

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np

delta = 0.025
x = np.arange(-3.0, 3.0, delta)
y = np.arange(-2.0, 2.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = np.exp(-X**2 - Y**2)
Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2)
Z = (Z1 - Z2) * 2

fig, ax = plt.subplots()
CS = ax.contour(X, Y, Z)
ax.clabel(CS, fontsize=10)
CS.set_color('k') # mess up the contour lines
plt.show()

Actual outcome

Expected outcome

Additional information

No response

Operating system

No response

Matplotlib Version

0.2.0.dev53887+unknown.g607d2c380.gc46efc9e5

Matplotlib Backend

No response

Python version

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Jupyter version

No response

Installation

None